D.K. Clock Shop storefront with white facade, red signage, and landscaping

What you need

  • The right cell. The size is printed on the old one.
  • A case knife for snap-off backs, or an adjustable case wrench for screw-down backs.
  • Plastic or non-magnetic tweezers.
  • A precision screwdriver if the back or the battery clip uses screws.
  • A soft cloth or a case holder so the crystal doesn't get scratched.

Steps

  1. Find the cell size. Look up your watch's movement or open the case and read the number on the old cell, such as 371, 377 or CR2025. The number is the size; SR (silver oxide) cells last longer in analog watches than alkaline ones.
  2. Identify the caseback. A snap-off back has a small notch on its edge. A screw-down back has notches spaced around it. Some backs are held by four or more small screws. Each needs a different tool.
  3. Open the case. Work on a soft cloth. Lever a snap-off back at the notch with a case knife, unscrew a screw-down back with a case wrench, or remove the screws with a precision screwdriver. Keep the gasket in its groove.
  4. Note how the cell sits. Before touching anything, take a photo. Note which side faces up and whether a clip or screw holds it. Some cells sit under an insulating sheet.
  5. Swap the cell. Release the clip and lift the old cell out with plastic tweezers. Metal tweezers can short the cell or the circuit. Drop in the new cell the same way up without touching its faces with your fingers.
  6. Check it runs. Watch the seconds hand for a minute. If it doesn't start, some movements need a reset: the movement sheet or the old cell's position usually shows an AC contact to touch briefly to the cell's top with tweezers.
  7. Reseal the case. Make sure the gasket is seated and undamaged, line up the back, and press or screw it closed. A dry, cracked or flattened gasket should be replaced.

When to take it to a shop instead

  • Dive and sports watches. Anything rated to 100 m or more needs a pressure test after the caseback has been off.
  • Luxury watches. A slipped case knife on a polished gold or steel back costs more to fix than a shop charges for the battery.
  • Sealed cases. Some fashion and plastic watches have backs that aren't meant to come off without a press.
  • A watch that ran fast or slow before the battery died. That points to a fault a new cell won't fix.

The watch repair directory lists shops near you, with whether they test water resistance.